The present invention relates generally to plasma cutting systems and, more particularly, to a method and apparatus for automatically controlling gas pressure for a plasma cutter.
Plasma cutting is a process in which an electric arc and plasma gas are used to cut or gouge a workpiece. Plasma cutters typically include a power source, a gas supply, such as compressed air, and a torch. The torch is constructed to create and maintain the plasma arc. To generate the plasma cutting power, a power source receives an input voltage from a transmission power receptacle or generator and provides output power to a pair of output terminals. One of the output terminals is connected to an electrode and the other is connected to the workpiece. An air supply is used with most plasma cutters to carry and propel the arc to the workpiece and assist in cooling the torch.
In order to operate properly, the plasma torch requires consistent, and preferably controllable air flow. Typically, this is provided by a system consisting of a pressure regulator; a downstream pressure gauge; a downstream, solenoid operated gas valve; and a downstream pressure limit switch. Using such a configuration, the operator is able to start and stop the gas flow as necessary, as well as access and adjust gas pressure settings to configure the plasma cutting system for a different cutting operation. While control of air pressure settings in this manner provides an operator with a great deal of control, such a construction is not without its drawbacks.
One drawback associated with existing gas pressure regulation systems, such as the one described above, is the imprecision associated with the use of mechanical regulators. An operator is required to manually check gas pressure and make adjustments by means of the pressure gauge and pressure regulator. Therefore, it would be preferable if a system were available that could dynamically control pressure regulation by an electronic means. Use of a control loop to control gas pressure, for example, could result in a more precisely tuned system and also allow for better accuracy and control of gas pressure. Such a system would also permit a faster transient response, or even allow for the gas pressure to be continuously altered, if need be.
Another drawback of existing systems is the inefficiency associated with the operator's need to adjust gas pressure settings. In a dynamic work environment, an operator may be required to perform gouging and cutting operations in a relatively continuous or alternating manner. The operator may be required to sequentially mix a plurality of cutting processes and a plurality of gouging processes. Suspending one process in order for the operator to check a pressure gauge and adjust the pressure setting for another operation is time consuming and results in overall process inefficiency. Therefore, it would be preferable if a system were available that would allow multiple pressure levels to be automatically and repeatedly set by means of multiple, selectable electrical switch positions, thus obviating the need for the user to make pressure adjustments.
In addition to providing dynamic control of the plasma torch/system for allowing multiple pressure levels to be automatically and repeatedly set by means of multiple, selectable electrical switch positions, it is also desired that the size and power requirements of the system be minimized. That is, a separate pressure regulator, pressure gauge, solenoid operated gas valve, and pressure limit switch typically included in a plasma torch can result in a bulky system that requires substantial power to operate. It would be preferable if a system were available that integrated the above listed separate elements. It would be further desirable if the power requirement to operate such an integrated system were lowered, to reduce associated operating costs.
It would, therefore, be desirable to design a plasma cutting system with simplified construction, operation, and control to ensure optimal pressure in the plasma torch, maximize efficiency and longevity in the plasma cutting system, and provide for reduced size and power requirements.